Piston and cylinder devices as such are used in a number of applications, for example in the form of positioning and maneuvering devices such as drive cylinders in order to maneuver movements in machines. The devices may also be in the form of shock absorbers to absorb and dampen movements between elements that are joined to pivot with each other. The above-mentioned types of piston and cylinder devices, independently of whether they are designed to be used as positioning and maneuvering devices or as shock absorbers, have in common that they display an inlet/outlet to each chamber such that the medium that is used can be added to and removed from the chambers. However, for a shock absorber, the inlet/outlet to each chamber of the piston- and cylinder device are connected together and designed as a common channel or passage such that the medium can flow forwardly and backwardly between the two chambers during the forward and backward motion of the piston device in the cylinder. On the other hand, in the type of piston and cylinder device that is used as a drive cylinder or positioning device, the inlet/outlet of each chamber are separate from each other and are each individually in flow-through connection with an external circuit that contains, among other things, devices for the control of the direction of some pressurized medium such as oil or air.
In the case of shock absorbers, the above-mentioned passage between the chambers is arranged in the actual piston device whereby the damping force that thus arises is mainly derived from the friction of the medium in the channel. The damping force can be regulated by varying the flow resistance or the speed and rate of flow with which the medium is allowed to flow forwardly and backwardly through the channel.
Recently, piston and cylinder devices have been developed with integral position-sensitive elements, that is, devices that make it possible to determine the motion of the piston device relative to the cylinder unit. The position-sensitive devices are usually connected to an external control unit, for example in the form of a computer. In the case of shock absorbers, the computer can be provided with the information that is required to control and regulate the damping properties or characteristic of the shock absorber in a way that is suitable for the application. For example, the damping force or characteristic of the shock absorber can be varied depending on the properties of the road surface, the speed, the terrain, the road slopes, vehicle tilt etc., or depending on parameters that are specified in advance, that is, if the vehicle is to offer a smooth and comfortable ride and thus offer high comfort for the travelers, or to allow more advanced and demanding driving. The computer can also be supplied with information about the speed, acceleration, etc., of the vehicle, in order to calculate an optimal damping characteristic of the shock absorber for the current driving conditions, based on the information that is supplied. The integral position-sensitive elements of the shock absorbers may also be used to measure the temperature of the medium that is exchanged between the two chambers of the shock absorber. If the properties of the medium that has been chosen to function in the shock absorber are previously known and these properties are stored in a computer, the measured temperature of the medium can be used to calculate its internal friction, or viscosity, at each instant. By regulating, based on this information, the speed and the rate of flow with which the medium is allowed to flow through the flow channel that exists between the two chambers of the shock absorber, the properties of the shock absorber can also be maintained essentially constant, independent of the temperature of the surroundings or of the shock absorber itself.
Piston and cylinder devices that are currently known have fairly complicated constructions in order to allow the medium to flow into and out from the chambers, and to make it possible to control and guide the movements of the piston and cylinder device.
One object of the invention is to achieve a piston and cylinder device that not only makes it possible for the medium to flow into and out from the chambers, but also allows in this part control and guidance of the movements of the piston in the piston and cylinder device.